Question: When you look at the nights sky, how many stars are actually there?

Tim Duckenfield answered on 5 Mar 2018:

Exactly how many stars we can see is a good question – really it depends where you are, how much light pollution there is from cities nearby etc. On a good day in the perfect location you can see thousands.

There was once a German astronomer called Heinrich Olbers, who thought about this question a lot in 1823 (though lots of people thought about it before he did, he gets a lot of the credit). He thought that there are infinitely many stars in the sky, in every direction, with each of the stars shining all the time. He argued that you should see a star in every possible direction, so the Earth should be flooded with light at night as if it were as bright as day time. This is clearly not happening! So we call this disagreement ‘Olber’s paradox’.
There are a few answers to Olber’s paradox, explaining why we only see some of the millions of stars we know exist in the night sky. One is that we think the universe isn’t infinitely old – it had a beginning, we call the Big Bang. Because it has only been around for about 13.7 billion years (only!), light from the furthest stars just haven’t had time to reach us yet! Secondly, we think that the universe is expanding. Imagine it like standing on a balloon, as it gets inflated. This makes all the light change as the universe expand, it changes colour from green to red, called ‘red-shifting’. After even more expansion, the light goes to a colour we can’t see with our eyes, but we can with special telescopes, and we call this colour ‘microwave’ (yes like the waves in your kitchen appliance). So we can’t see this light in the sky with our eyes, it looks dark. Luckily for star-gazers, there are plenty of stars still visible even after these effects.